The mechanical environment of the chondrocytes is one of the most important factors affecting the health and function of the diarthrodial joint. Under normal physiologic conditions, chondrocytes utilize mechanical signals in conjunction with genetic and biochemical factors to maintain the articular cartilage extracellular matrix. However, abnormal loading conditions such as excessive stresses or alterations in joint loading are believed to be significant factors in the initiation and progression, of joint disease. The sequence of mechanical and biochemical events regulating these signal transduction processes in vivo are still unclear, although indirect evidence suggests that cellular deformation serves as a primary regulatory signal. The central hypothesis of this project is that cyclic deformation of the chondrocytes regulates the transduction of mechanical loads to a biochemical response through two pathways: the actin cytoskeleton and the calcium ion (Ca2+) second messenger system. It is hypothesized that deformation of the cytoskeleton and the chondrocyte nucleus are responsible for regulating changes in proteoglycan synthesis rates, while deformation-induced ca2+ waves regulate the expression of the chondroitin sulfate 3-B-3(-) epitope, considered to be a marker of early osteoarthritis. The goals of the proposed project will be accomplished using a bovine articular cartilage explant model loaded in pure torsion. This loading configuration differs from all previously used systems in that it will result in purely deviatoric deformation within the explant (i.e., deformation without volume changes), allowing isolation of the effects of cell and tissue deformation from those of most other physical factors (e.g., fluid flow, fluid and osmotic pressures, streaming potentials, etc.). The following specific aims will be performed: l) Quantify the relationship between the magnitude, duration and frequency of cyclic torsion on proteoglycan synthesis rates and 3-B-3(-) expression using autoradiography and immunolocalization; 2) Determine the role of the actin cytoskeleton in mechanical transduction using chemical agents which disrupt actin microfilaments; 3) Determine the role of deformation-induced Ca2+ waves in mechanical transduction using inhibitors of Ca2+ mobilization. The long term goals of this study are to determine the roles of mechanical factors in regulating cartilage metabolism under normal or abnormal conditions and to identify the signal transduction pathways. A better understanding of these pathways will lead to the development of pharmaceutical or biophysical interventions for the treatment of osteoarthritis.